Chi X et al. (2020), Fitness benefits and costs of shelters to the s...

ECB-ART-49846

PeerJ 2020 Jan 01;8:e8886. doi: 10.7717/peerj.8886.

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Fitness benefits and costs of shelters to the sea urchin Glyptocidaris crenularis.

Chi X , Sun J , Yu Y , Luo J , Zhao B , Han F , Chang Y , Zhao C .

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Understanding the ecological role of shelters is greatly hampered by the scarcity of long-term laboratory experiments on the trade-off between fitness benefits and costs. This lack probably leads to an underestimation of the negative and/or positive effects on behaviors and growth of marine invertebrates in benthic ecosystems. Although our previous study revealed a significant effect on fitness-related traits of Glyptocidaris crenularis after 31 months, the present study extended it and investigated fitness benefits and/or costs of long-term sheltering on sea urchins to over 7 years. The present long-term study suggests that the previously reported reduction in feeding rate probably resulted from a reduction in reflexive feeding motions (Aristotle's lantern reflex) rather than changes in foraging behavior. Actively seeking sheltering behavior was negatively impacted in individuals with continuous access to shelters. However, covering and righting behaviors did not differ in sheltered sea urchins, indicating that these behaviors are maintained to escape from adverse environments regardless of shelter. Body size of sea urchins in the group with shelters was significantly lower than those without shelters after 7 years. Weights of gonads and gut were not significantly different after 7 years despite previous observations of differences after ~2.5 years. The present study provides valuable information on the trade-off between fitness benefits and costs to sea urchins residing in shelters. However, the present study is only a laboratory investigation for one urchin species (G. crenularis) which does not consider the complexity of natural environments. Field studies should be carried out with G. crenularis and other sea urchin species, before a more universal conclusion can be drawn.

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References [+] :

Byrne, Warming influences Mg2+ content, while warming and acidification influence calcification and test strength of a sea urchin. 2014, Pubmed, Echinobase

	Figure 1. Diagrams showing the experimental devices for the measurements of righting behavior (A), Aristotle’s lantern reflex (B), covering behavior (C), foraging behavior (D) and sheltering behavior (E).
	Figure 2. Righting response time (A) and Aristotle’s lantern reflex (B) of Glyptocidaris crenularis in different experimental groups 5 min after the beginning of observations (N = 5 for righting response, N = 4 for Aristotle’s lantern reaction mean ± SD).Letters above the bars represent significance (P < 0.05).
	Figure 3. Time to first covering (A), number of shells used for covering (B), covered areas of sea urchins (C) and percentage of covered areas (D) of Glyptocidaris crenularis in different experimental groups in 1 hour after the beginning of experiment (N = 5, mean ± SD).
	Figure 4. Movement and foraging behavior: total distance of movement (A), velocity (B), acceleration (C) and foraging time (D) of Glyptocidaris crenularis in different experimental groups 30 minutes after the beginning of observations (N = 5, mean ± SD).
	Figure 5. Duration in sheltered areas of Glyptocidaris crenularis in different experimental groups during 30 min after the beginning of experiment (N = 5, mean ± SD).Letters above the bars represent significance (P < 0.05).
	Figure 6. Test diameter (A), body weight (B) and test height: test diameter (C) of Glyptocidaris crenularis in different experimental groups (N = 5, mean ± SD).Letters above the bars represent significance (P < 0.05).
	Figure 7. Test weight (A), test thickness (B), lantern weight (C) and lantern length (D) of Glyptocidaris crenularis in different experimental groups (N = 5, mean ± SD).Letters above the bars represent significance (P < 0.05).
	Figure 8. Gut weight (A) and gonads weight (B) of Glyptocidaris crenularis in different experimental groups (N = 5, mean ± SD).